The invention relates to a thrust dynamic pressure bearing in which herringbone-type dynamic pressure generating grooves are formed in a thrust bearing face.
Conventionally, as shown in FIGS. 2(A) and 2(B), in such a kind of thrust dynamic pressure bearing, each of herringbone-type dynamic pressure generating grooves 102 formed in a thrust bearing face 101 has a uniform depth h.
When the depth of a herringbone-type dynamic pressure generating groove is uniform as in the prior art, however, it has been known that a lubricant fluid cannot be efficiently gathered into a radially center portion of the herringbone-type dynamic pressure generating groove, because of the influence of a centrifugal force generated during the rotation or the like, and hence the load ability cannot be maximized.
It is an object of the invention to provide a thrust dynamic pressure bearing in which a lubricant fluid can be efficiently gathered into a radially center portion of a herringbone-type dynamic pressure generating groove, so that the load ability can be maximized.
The inventors have noted the fact that the centrifugal force generated during the rotation which acts on a lubricant fluid in a thrust bearing face varies depending on positions in a radial direction, thereby configuring the invention.
That is, the thrust dynamic pressure bearing of the invention is characterized in that, in a thrust dynamic pressure bearing in which herringbone-type dynamic pressure generating grooves are formed in a thrust bearing face,
a depth of an inner circumference portion of each of the dynamic pressure generating grooves is larger than a depth of a radially center portion of the dynamic pressure generating groove, and a depth of a radially outer circumference portion of the dynamic pressure generating groove is larger than the depth of the inner circumference portion.
In the thrust dynamic pressure bearing of the invention the depth of each of the dynamic pressure generating grooves in the outer circumference portion in which the centrifugal force is strongest is made largest, so that the ability of gathering the lubricant fluid toward the center portion of the herringbone-type dynamic pressure generating groove is maximized. The dynamic pressure generating groove in the inner circumference portion in which the centrifugal force is weakest but the ability of gathering the lubricant fluid toward the center portion is required has the second largest depth. Therefore, the ability of gathering the lubricant fluid toward the center portion of the herringbone-type dynamic pressure generating groove is balanced between the outer circumference portion and the inner circumference portion. The center portion of the herringbone-type dynamic pressure generating groove into which the lubricant fluid is gathered because of the herringbone shape of the dynamic pressure generating groove is shallowest.
According to this configuration, the lubricant fluid can be efficiently gathered into the radially center portion of the dynamic pressure generating groove, and the load ability can be maximized.